The present invention relates in general, to separation systems and, in particular, to a new and useful method and apparatus for separating a multiple phase mixture into separate vapor and liquid phases utilizing single or multiple pairs of centrifugal force separators. The present invention is particularly suited for applications involving the separation of oil and gas phases contained in wellhead fluids obtained from hydrocarbon production systems. The present invention can be employed either topside or in subsea locations.
Most of the known gas/oil separation systems rely on natural or gravity separation which requires large vessels to achieve the desired separation performance. When natural separation is used in a relatively small vessel, the throughput or vapor flux of that system is significantly smaller when compared to other systems not relying on natural separation. An example of a system which apparently uses natural separation is described in U.S. Pat. No. 4,982,794.
One known separation system is disclosed in UK Patent Application No. GB 2 203 062 A and uses centrifugal separation for a primary separation stage and inertial separation (i.e., scrubbers) for a second stage of separation. Although this system most likely has higher separation capacities than a system relying on natural separation, it most likely has less capacity when compared to a system that could employ centrifugal separation for both stages.
Presently, there is no known gas/oil separation system or method for separating a multiple phase mixture of oil and gas into separate vapor and liquid phases utilizing single or multiple pairs of centrifugal force separators.
The present invention is drawn to a method and apparatus particularly suited for separating a wellhead fluid mixture containing oil and gas phases obtained from hydrocarbon production systems into its constituent parts. The present invention can be employed either topside or in subsea applications through the use of a compact and highly efficient separator arrangement.
More particularly, one aspect of the present invention is drawn to a separation apparatus which utilizes one or more curved-arm, centrifugal force, primary separator(s) and one or more cyclone, centrifugal force, secondary separator(s). Except for some changes made to the curved-arms, the primary separator is very similar to the separator described in U.S. Pat. No. 4,648,890 to Kidwell et al., assigned to The Babcock and Wilcox Company. The secondary separator is similar to the separator described in U.S. Pat. No. 3,324,634 to Brahler et al., also assigned to The Babcock and Wilcox Company. The primary and secondary separators are always employed in pairs, and the combination of a centrifugal-type primary and secondary separator as utilized by the present invention provides a compact and highly-efficient separator arrangement. The separator apparatus can be used in multiple pairs (two or more primary and two or more secondary separators) or in an apparatus having only a single primary and a single secondary separator. The multiple pair arrangement would be typically used for topside applications while the single primary/single secondary separator arrangement would typically be sufficient to satisfy most subsea applications.
Another aspect of the present invention is drawn to a method for separating a wellhead fluid mixture obtained from hydrocarbon production systems containing oil and gas phases into its constituent parts, using the broad concepts discussed above.
Currently, topside or platform separation is normally performed using gravity separation which requires very large drum or pressure vessel volumes. Not only is the present invention less costly to fabricate due to its smaller size than known separation devices, but the reduced size of the gas/oil separator of the present invention thus requires less platform space, an economically attractive feature since the cost of platforms is directly related to the size of the vessels.
The present invention also provides a unique and efficient compact apparatus for subsea separation of a gas and liquid mixture. In a subsea application, the present invention provides the most benefit for marginal field developments because without subsea separation, marginal fields may become economically unfeasible to operate.
As is well-known, subsea separation provides for the separation of vapor and liquid phases prior to transporting the fluids to a platform or production facility. Fewer technical challenges are involved with first separating the phases and then separately transporting them downstream as compared to transporting a multi-phase mixture of gas and oil where slugging and hydrate formation issues are prevalent.
Presently, no other apparatus is known which provides a combination of centrifugal force primary and secondary separators having the compactness and high capacity separation efficiency of the present invention.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific results attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.